This invention relates to a back lighting device for illuminating transmissive or semi-transmissive panels from the rear side.
Recently, liquid crystal display devices with a back lighting mechanism which are thin and allow easy viewing of information, have been used with lap-top or book type word processors or computers. The back lighting mechanism in common use adopts an "edge lighting" method in which a linear light source, such as a fluorescent tube, is provided at one end portion of a transmissive light conducting plate as shown in FIG. 1. Further, as shown in FIG. 2, one surface of the light conducting plate is often partially covered with a light diffusing material having a higher refractive index than the material of the light conducting plate, and the one surface thus covered is almost entirely covered with a specular reflecting plate or light diffusing/reflecting plate.
On the other hand, in order to improve the performance of word processors or personal computers, there have been strong demands for. miniaturization, improvement in visibility, and increase in the efficiency of the conversion of power to luminance thereof.